Interpretive Summary: Relaxation of IGF2 imprinting (i.e. substantial expression from the normally silent maternally inherited allele) is fairly prevalent and implicated in human cancer and various developmental diseases. The causes of IGF2 relaxation of imprinting, however, are unknown. Using mice, we tested whether post-weaning diet affects allelic expression and CpG methylation of Igf2. Our results indicate that subtle dietary differences in the post-weaning period can permanently affect expression and methylation of Igf2, suggesting that diet during childhood could contribute to relaxation of IGF2 imprinting in humans.

Technical Abstract:
IGF2 loss of imprinting (LOI) is fairly prevalent and implicated in the pathogenesis of human cancer and developmental disease; however, the causes of this phenomenon are largely unknown. We determined whether the post-weaning diet of mice affects allelic expression and CpG methylation of Igf2. C57BL/6JxCast/EiJ F1 hybrid mice were weaned onto (1) a standard natural ingredient control diet, (2) a synthetic control diet or (3) a synthetic methyl-donor-deficient diet lacking folic acid, vitamin B12, methionine and choline. Maternal Igf2 expression in kidney was negligible at birth, but increased to 10% of total expression after 60 days on the natural control diet. By 60 days post-weaning, both synthetic diets caused significant LOI of Igf2 relative to animals weaned onto the natural control diet. Total Igf2 expression was significantly reduced in these groups, however, indicating that the increase in relative maternal Igf2 expression was caused by specific down-regulation of the paternal allele. The LOI induced by the synthetic-deficient diet persisted during a subsequent 100-day 'recuperation' period on natural ingredient diet. There were no group differences in overall or allele-specific CpG methylation in the H19 differentially methylated region (DMR), Igf2 DMR0 or Igf2 DMR1. At 30 and 60 days post-weaning, however, the paternal allele of Igf2 DMR2 was hypermethylated in the kidneys of mice on the control synthetic diet. These results indicate that post-weaning diet can permanently affect expression of Igf2, suggesting that childhood diet could contribute to IGF2 LOI in humans.